Oxide semiconductor, semiconductor device, semiconductor memory device, and solid-state imaging device

ABSTRACT

According to one embodiment, an oxide semiconductor includes indium (In), gallium (Ga), and silicon (Si). A composition ratio of Si to In (Si/In) in the oxide semiconductor is larger than 0.2, and a composition ratio of Si to Ga (Si/Ga) in the oxide semiconductor is larger than 0.2.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2016-179805, filed on Sep. 14, 2016; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an oxide semiconductor,a semiconductor device, a semiconductor memory device, and a solid-stateimaging device.

BACKGROUND

In a semiconductor device, an oxide semiconductor including amulti-element compound is sometimes used. For example, as an oxidesemiconductor having a high carrier conductivity, InGaZnO has been knownand applied to a channel layer of a thin film transistor (TFT). Theoxide semiconductor has been required to improve, for example, its heatresistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating an oxide semiconductoraccording to a first embodiment;

FIG. 2 is a table showing conditions for forming the oxide semiconductoraccording to the first embodiment and the composition thereof;

FIG. 3 is a graph illustrating an infrared absorption spectrum of theoxide semiconductor according to the first embodiment;

FIG. 4 is a graph illustrating the state of the oxide semiconductor;

FIG. 5 is a table showing a calculation model used in a simulationanalysis of the oxide semiconductor according to the first embodiment;

FIG. 6A to FIG. 6C are views showing simulation results for the localstructure of the oxide semiconductor according to the first embodiment;

FIG. 7A to FIG. 7C are views showing simulation results for the localstructure of the oxide semiconductor according to the first embodiment;

FIG. 8A to FIG. 8C are graphs showing simulation results for the localstructure of the oxide semiconductor according to the first embodiment;

FIG. 9A and FIG. 9B are graphs showing simulation results for the localstructure of the oxide semiconductor according to the first embodiment;

FIG. 10A and FIG. 10B are graphs illustrating simulation results of theoxide semiconductor according to the first embodiment;

FIG. 11 is a schematic view illustrating the local structure of theoxide semiconductor;

FIG. 12A to FIG. 12F are graphs showing simulation results of anelectronic state of the oxide semiconductor according to the firstembodiment;

FIG. 13A to FIG. 13D are graphs showing simulation results of the oxidesemiconductor according to the first embodiment and an oxide of areference example;

FIG. 14 is a schematic sectional view illustrating a semiconductordevice according to a second embodiment;

FIG. 15 is a schematic sectional view illustrating another semiconductordevice according to the second embodiment;

FIG. 16 is a schematic sectional view illustrating the firstsemiconductor layer of the semiconductor device according to the secondembodiment;

FIG. 17 is a schematic sectional view illustrating another firstsemiconductor layer of the semiconductor device according to the secondembodiment;

FIG. 18 is a schematic sectional view illustrating a solid-state imagingdevice according to a third embodiment; and

FIG. 19 is a schematic sectional view illustrating a semiconductormemory device according to a fourth embodiment.

DETAILED DESCRIPTION

According to one embodiment, an oxide semiconductor includes indium(In), gallium (Ga), and silicon (Si). A composition ratio of Si to In(Si/In) in the oxide semiconductor is larger than 0.2, and a compositionratio of Si to Ga (Si/Ga) in the oxide semiconductor is larger than 0.2.

Various embodiments will be described hereinafter with reference to theaccompanying drawings.

The drawings are schematic and conceptual; and the relationships betweenthe thickness and width of portions, the proportions of sizes amongportions, etc., are not necessarily the same as the actual valuesthereof. Further, the dimensions and proportions may be illustrateddifferently among drawings, even for identical portions.

In the specification and drawings, components similar to those describedor illustrated in a drawing thereinabove are marked with like referencenumerals, and a detailed description is omitted as appropriate.

First Embodiment

FIG. 1 is a schematic sectional view illustrating an oxide semiconductoraccording to a first embodiment.

In an example shown in FIG. 1, an oxide semiconductor 55 according tothe embodiment is provided on a substrate 10. The substrate 10 is, forexample, a silicon substrate, a glass substrate, or a plastic substrate.As the substrate 10, a substrate including a resin such as polyimide maybe used. The substrate 10 may be impermeable to light. The oxidesemiconductor 55 includes indium (In), gallium (Ga), silicon (Si), andoxygen (O). The oxide semiconductor 55 is, for example, a ternary oxidein an amorphous (non-crystalline) state, and an InGaSi-based oxideincluding In, Ga, Si, and O as main constituent elements.

When a ratio of a composition of Si in the oxide semiconductor 55 to acomposition of In in the oxide semiconductor 55 is represented by Si/In,Si/In>0.2 in the oxide semiconductor 55. That is, a ratio of the numberof Si atoms included in a region (region R1) in the oxide semiconductor55 to the number of In atoms included in the region R1 is larger than0.2.

When a ratio of a composition of Si in the oxide semiconductor 55 to acomposition of Ga in the oxide semiconductor 55 is represented by Si/Ga,Si/Ga>0.2 in the oxide semiconductor 55. That is, a ratio of the numberof Si atoms included in a region (region R1) in the oxide semiconductor55 to the number of Ga atoms included in the region R1 is larger than0.2.

When the content ratio of Si to the sum of a composition of In, acomposition of Ga, and a composition of Si in the oxide semiconductor 55is represented by Si/(In+Ga+Si), SigIn+Ga+Si)>0.09 in the oxidesemiconductor 55. The ratio of the number of Si atoms to the sum of thenumber of In atoms, the number of Ga atoms, and the number of Si atomsis higher than 0.09. That is, in the region R1 of the oxidesemiconductor 55, the content ratio of Si to the sum of the number of Inatoms, the number of Ga atoms, and the number of Si atoms is larger than9 atomic %. At this time, for example, the composition of In and thecomposition of Ga can be made approximately equal. That is, when thecomposition ratio of In to Ga is represented by In/Ga, in the oxidesemiconductor 55, In/Ga can be made approximately 1. For example, In/Gais not less than 0.8 and not more than 2.0.

In the case where an oxide semiconductor is used as a channel layer of athin film transistor, the oxide semiconductor is formed using, forexample, a sputtering method. When the oxide semiconductor is formedusing a sputtering method, for example, a mixed gas of argon (Ar) gasand oxygen (O₂) gas is used. For example, there is a reference examplein which as the oxide semiconductor, amorphous InGaZnO is formed using asputtering method. In this reference example, the composition (contentratio) of the main element included in InGaZnO greatly varies dependingon the ratio of the flow rate of Ar gas to the flow rate of O₂ gas.Further, in amorphous InGaZnO, desorption of oxygen, zinc, or the likemay occur in a heat treatment at a relatively low temperature. For thisreason, it is difficult to control the chemical bonding state ofconstituent elements in amorphous InGaZnO. Therefore, in the case whereInGaZnO is used as a channel layer of a thin film transistor, avariation or change in threshold voltage is likely to occur, and theelectrical properties are not stable in some cases.

On the other hand, the oxide semiconductor 55 according to theembodiment includes In, Ga, and Si. The inventors of the applicationfound that the heat resistance of the oxide semiconductor can be greatlyimproved by the above-mentioned composition. For example, in the oxidesemiconductor 55, a change in electrical properties (for example,electrical resistivity) due to a heat treatment is smaller than in anoxide semiconductor such as InGaZnO. By controlling the compositionratio of In, Ga, and Si to an appropriate value, an oxide semiconductorhaving a large carrier conductivity is obtained. It becomes easy tocontrol the composition of the oxide semiconductor or the chemicalbonding state. In the case where the oxide semiconductor 55 is used in asemiconductor device such as a transistor, the stability of theproperties of the semiconductor device can be improved. Hereinafter,studies by the inventors of the application will be described.

FIG. 2 is a table showing conditions for forming the oxide semiconductoraccording to the first embodiment and the composition thereof.

The oxide semiconductor 55 (samples 1 to 6) shown in FIG. 2 is formed bya DC magnetron sputtering method. The thickness of each of the samples 1to 6 is about 100 nm. In FIG. 2, conditions during the sputtering,conditions for a heat treatment after film formation by sputtering,compositions (atomic %), and composition ratios are shown. In thesputtering, an InGaSiO target (sintered body) is used. The compositionratio of this target is In:Ga:Si=1:1:0.5. In the sputtering, a mixed gasof Ar and O₂ is used, and the pressure is set to not less than 0.32pascal (Pa) and not more than 0.38 Pa. The output of a DC power supplyto be used in the sputtering is set to 300 watts (W), and the substrateis not heated during the sputtering.

In the sample 1 to the sample 3, the flow rate ratio of O₂ gas duringthe sputtering is 3.2%. In the sample 4 to the sample 6, the flow rateratio of O₂ gas during the sputtering is 18.9%. Incidentally, the flowrate ratio of O₂ gas is represented by a percentage of the flow rate ofO₂ gas to the sum of the flow rate of Ar gas and the flow rate of O₂ gas(O₂/Ar+O₂). That is, each of the sample 1 to the sample 3 is the oxidesemiconductor 55 formed under low oxygen conditions during thesputtering. Each of the sample 4 to the sample 6 is the oxidesemiconductor 55 formed under excess oxygen conditions during thesputtering. The sample 2 and the sample 5 are subjected to a heatingtreatment at 420° C. for 60 minutes in an inert gas atmosphere includingargon after the sputtering. The sample 3 and the sample 6 are subjectedto a heating treatment at 420° C. for 60 minutes in a nitrogen gasatmosphere including hydrogen (3 wt %) having a strong reducing propertyafter the sputtering. The sample 1 and the sample 4 are not subjected toa heating treatment.

In the compositional analysis of the sample 1 to the sample 6,Rutherford backscattering spectrometry and hydrogen forward scatteringspectrometry are used. As an analyzer, Pelletron 3SDH manufactured byNational Electrostatics Corporation is used. The analytical accuracy(atomic %) of the compositions of this device is ±0.2 for In, ±0.3 forGa, ±0.3 for Si, ±1 for O, ±0.2 for H, and ±0.13 for Ar.

In the sample 1 which is formed under low oxygen conditions and is notsubjected to a heat treatment, the composition of In is 16.3 atomic %,the composition of Ga is 15.8 atomic %, the composition of Si is 6.7atomic %, and the composition of O is 60.1 atomic %. In the sample 1,the content ratio of Si is about 17.3 atomic % (Si/(In+Ga+Si) is about0.173), and In/Ga is about 1. In the sample 4 which is formed underexcess oxygen conditions and is not subjected to a heat treatment, thecomposition of In is 16.0 atomic %, the composition of Ga is 15.5 atomic%, the composition of Si is 6.8 atomic %, and the composition of O is59.0 atomic % In the sample 4, the content ratio of Si is about 17.8atomic % (Si/(In+Ga+Si) is about 0.178), and In/Ga is about 1.

When comparing the sample 1 with the sample 4, it is found that thecomposition of each of the elements (In, Ga, Si, and O) other thanimpurities (H and Ar) does not change much with respect to the flow rateratio of O₂ gas during the sputtering. With respect to the samples 1 to3 formed under low oxygen conditions, when comparing the sample 1 whichis not subjected to a heat treatment, the sample 2 which is subjected toa heat treatment in an inert gas atmosphere including argon, and thesample 3 which is subjected to a heat treatment in a nitrogen gasatmosphere including hydrogen (3 wt %) having a strong reducingproperty, it is found that the composition of each of the elements (In,Ga, Si, and O) other than impurities (H and Ar) hardly depends on theheat treatment conditions. With respect to the samples formed underexcess oxygen conditions, when comparing the sample 4 which is notsubjected to a heat treatment, the sample 5 which is subjected to a heattreatment in an inert gas atmosphere including argon, and the sample 6which is subjected to a heat treatment in a nitrogen gas atmosphereincluding hydrogen (3 wt %) having a strong reducing property, it isfound that the composition of each of the elements (In, Ga, Si, and O)other than impurities (H and Ar) hardly depends on the heat treatmentconditions. In all samples, the composition of each of the elementsother than impurities in the depth direction is substantially constant.

FIG. 3 is a graph illustrating an infrared absorption spectrum of theoxide semiconductor according to the first embodiment.

In FIG. 3, an infrared absorption spectrum of the sample 1 formed underlow oxygen conditions and an infrared absorption spectrum of the sample4 formed under excess oxygen conditions are shown. Both of the sample 1and the sample 4 are not subjected to a heat treatment after thesputtering. In the measurement of the infrared absorption spectrum,FT-IR, IFS-66v/S manufactured by Bruker Corporation is used. Thevertical axis represents an absorbance (arbitrary unit) of the sample.The horizontal axis represents the wavenumber (cm⁻¹) of the infraredradiation.

In each of the sample 1 and the sample 4, an absorption based onMetal-O—Si stretching vibration occurs at a wavenumber of around 930cm⁻¹. Such an absorption peak was found to be a spectrum derived from atleast one of an In—O—Si bond and a Ga—O—Si bond. Also in the samplessubjected to a heat treatment (sample 2, sample, 3, sample 5, and sample6), a similar infrared absorption spectrum as that of the sample 1 andthe sample 4 is obtained. From these results, it is considered that anIn atom and an Si atom are bonded by sharing an O atom. That is, one Oatom is bonded to an In atom and also bonded to an Si atom. Similarly,it is considered that a Ga atom and an Si atom are bonded by sharing anO atom. That is, one O atom is bonded to a Ga atom and also bonded to anSi atom. For example, it is presumed that in the oxide semiconductor 55,a structural body in which an In—O cluster and an Si—O cluster areconnected, and a structural body in which a Ga—O cluster and an Si—Ocluster are connected exist. Incidentally, as a result of analyzingcrystallinity using X-ray diffractometry, it was found that the oxidesemiconductor 55 (sample 1 to sample 6) is in an amorphous state bothbefore and after the heat treatment.

The bond dissociation energy (kilojoules/mole: kJ/mol) of a diatomicmolecule which is regarded as an index of bond strength is as follows:800 Id/mol for Si—O, 374 Id/mol for Ga—O, 346 kJ/mol for In—O, and 250kJ/mol for Zn—O. The bond dissociation energy for an Si—O bond is twiceor more the bond dissociation energy for the other bonds. As describedabove, the oxide semiconductor 55 includes at least one of an In—O—Sibond and a Ga—O—Si bond. Due to this, for example, oxygen deficiencyhardly occurs in the oxide semiconductor 55, and high heat resistance isobtained.

For example, in the case where amorphous InGaZnO is formed using asputtering method, the composition of a main constituent element islikely to greatly vary depending on the gas conditions duringsputtering. Further, in the heat treatment after sputtering, desorptionof oxygen or the like occurs in some cases. On the other hand, in thecase of a ternary oxide including In, Ga, and Si, the composition ofInGaSiO (the composition ratio of each of In, Ga, Si, and O) does notchange much with respect to the flow rate ratio of O₂ gas duringsputtering, and hardly depends on the heat treatment conditions aftersputtering. Further, InGaSiO is hardly crystallized also after the heattreatment and maintains the amorphous state.

FIG. 4 is a graph illustrating the state of the oxide semiconductor.

The vertical axis in FIG. 4 represents a state (ST) of the oxidesemiconductor (InGaSiO), and the horizontal axis in FIG. 4 representsSi/Ga (or Si/In). As shown in FIG. 4, InGaSiO can take two states (astate ST1 and a state ST2) depending on Si/Ga. The state ST1 is a statein which the number of Si atoms per five Ga atoms is 1 or less inInGaSiO. The state ST2 is a state in which the number of Si atoms perfive Ga atoms is more than 1 in InGaSiO.

In InGaSiO, one Ga atom is bonded to a plurality of oxygen atoms. Asdescribed later, the coordination number of a Ga atom in InGaSiO ismainly 4 or 5. Therefore, the state ST2 in which the number of Si atomsper five Ga atoms is more than 1 is, for example, a state in which eachof the Ga atoms in InGaSiO is likely to form a Ga—O—Si bond. Asdescribed above, the bond dissociation energy for an Si—O bond is high,and therefore, the Ga—O—Si bond is stable to heat. Therefore, it isconsidered that the heat resistance of InGaSiO can be improved bysetting Si/Ga>0.2 as in the state ST2.

Similarly, a state in which the number of Si atoms per five In atoms ismore than 1 in InGaSiO is a state in which each of the In atoms inInGaSiO is likely to form an In—O—Si bond. Therefore, it is consideredthat the heat resistance of InGaSiO can be improved by settingSi/In>0.2. As described above, in the embodiment, In/Ga can be set toabout 1. At this time, in the state ST2, Si/(In+Ga+Si)>0.09.

In order to clarify the structure and electronic state of InGaSiO, alocal structure analysis and an electronic state analysis were performedfor InGaSiO in an amorphous state using a molecular dynamics method andfirst-principles calculation. By doing this, an effect brought about bySi in a ternary oxide of In, Ga, and Si was studied in detail.

FIG. 5 is a table showing a calculation model used in a simulationanalysis of the oxide semiconductor according to the first embodiment.

Three types of calculation models of InGaSiO were used. FIG. 5 shows thenumber of atoms (atoms) and composition ratio in each calculation model.

In each calculation model, the total number of atoms is 90 to 92 atoms.In InGaSiO, an In—O cluster and a Ga—O cluster are, for example,connected with a given regularity, and each of the In—O cluster and theGa—O cluster is considered to share part of oxygen atoms with an Si—Ocluster. Based on this, In/Ga was set to 1. The number of O (oxygen)atoms was set to a value that satisfies charge neutralization conditionsin all models in consideration of the valence of each of In, Ga, and Si.A simulation model of an amorphous structure was fabricated by a meltand quench method in which classical molecular dynamics calculation andfirst principle molecular dynamics calculation are combined. Withrespect to each calculation model, a local structure analysis at atemperature of 300 K was performed using a first principle moleculardynamics method. Thereafter, the electronic state was analyzed by firstprinciple calculation to which a hybrid functional was applied.

In a model L, the number of In atoms is 16, the number of Ga atoms is16, the number of Si atoms is 4, and the number of O (oxygen) atoms is56. In the model L, the content ratio of Si is 11.1 atomic %(Si/(In+Ga+Si)=0.111). With respect to the composition ratio of Si, eachof Si/In and Si/Ga is 0.25. With respect to the composition ratio of Inand Ga, In/Ga is 1.

In a model R, the number of In atoms is 14, the number of Ga atoms is14, the number of Si atoms is 7, and the number of O (oxygen) atoms is56. In the model R, the content ratio of Si is 20.0 atomic %(Si/(In+Ga+Si)=0.2). With respect to the composition ratio of Si, eachof Si/In and Si/Ga is 0.5. With respect to the composition ratio of Inand Ga, In/Ga is 1.

In a model U, the number of In atoms is 12, the number of Ga atoms is12, the number of Si atoms is 10, and the number of O (oxygen) atoms is56. In the model U, the content ratio of Si is 29.4 atomic %(Si/(In+Ga+Si)=0.294). With respect to the composition ratio of Si, eachof Si/In and Si/Ga is 0.833. With respect to the composition ratio of Inand Ga, In/Ga is 1.

As described above, in the three types of calculation models shown inFIG. 5, the ratio occupied by Si in the three elements of In, Ga, and Siis mutually different. The content ratio of Si in the model L is lowerthan the content ratio of Si in the model U. The content ratio of Si inthe model R is between them.

FIG. 6A to FIG. 6C and FIG. 7A to FIG. 7C are views showing simulationresults for the local structure of the oxide semiconductor according tothe first embodiment.

FIG. 6A to FIG. 6C show the distribution of coordination number in afirst coordination of each of an In atom, a Ga atom, and an Si atom inInGaSiO having an amorphous structure. FIG. 6A shows the results of themodel L, FIG. 6B shows the results of the model R, and FIG. 6C shows theresults of the model U.

FIG. 7A is a graph showing the results of FIG. 6A to FIG. 6C as arelationship between the content ratio of Si and the averagecoordination number of Ga. FIG. 7B is a graph showing the results ofFIG. 6A to FIG. 6C as a relationship between the content ratio of Si andthe average coordination number of In. FIG. 7C is a table showingnumerical values of the plots shown in FIG. 7A and FIG. 7B.

Here, the atom was assumed to be a hard sphere. Based on the radialdistribution function (which will be described later with respect toFIGS. 8 and 9), normalization was performed by the number of O atomspresent within a range with a radius of 0.26 nanometers (nm) from theatom of interest. By analyzing the coordination number in the firstcoordination of each of an In atom, a Ga atom, and an Si atom, thecoordination structure of an oxide cluster constituting the oxidesemiconductor can be identified.

With respect to Si, 4 coordination is dominant in all models, andtherefore, Si in InGaSiO is presumed to form an Si—O cluster having atetrahedral structure regardless of the composition. On the other hand,with respect to In, it was found that the average coordination numberdecreases with an increase in the content ratio of Si, and a part oftypical 6 coordination (octahedron) changes to 5 coordination(pentahedron or hexahedron). On the other hand, with respect to Ga, itwas found that in the case where the content ratio of Si is set to 29.4atomic %, the average coordination number largely decreases and theproportion of a Ga—O cluster composed of 4 coordination (tetrahedron)excessively increases.

From the results of the coordination number analysis, it is interpretedthat since the Si—O cluster forms a robust tetrahedral structureregardless of the composition, in the case where the composition of Siis changed in InGaSiO, In and Ga change the coordination structure,thereby achieving structural relaxation. In the model U including muchSi, the Ga—O cluster having a low coordination structure is excessivelyformed, and therefore, it is presumed to be in a geometrically unstablestate.

As described previously with respect to FIG. 4, in InGaSiO, byincreasing the composition ratio of Si, a Ga—O—Si bond and an In—O—Sibond are likely to be formed, and heat resistance can be improved. Onthe other hand, for example, as shown in FIG. 7A, when the compositionratio of Si (the content ratio of Si) is set to too high, the Ga—Ocluster having a low coordination structure is increased, and therefore,it is considered that the oxide semiconductor becomes unstable. FromFIG. 7A, the content ratio of Si is preferably 20 atomic % or less. Thatis, it is preferred to satisfy Si/(In+Ga+Si)≦0.2. For example, in theregion R1 of the oxide semiconductor 55, the content ratio of Si to thesum of the number of In atoms, the number of Ga atoms, and the number ofSi atoms is preferably 20 atomic % or less.

At this time, Si/Ga≦0.5. For example, the ratio of the number of Siatoms included in the region R1 to the number of Ga atoms included inthe region R1 in the oxide semiconductor 55 is 0.5 or less. Si/In≦0.5.For example, the ratio of the number of Si atoms included in the regionR1 to the number of In atoms included in the region R1 in the oxidesemiconductor 55 is 0.5 or less.

At this time, In/Ga is 1. The average coordination number of Ga inInGaSiO is 4.5 or more, and the average coordination number of In is5.15 or more. As described above, it is considered that the Si—O clusterforms a robust tetrahedral structure regardless of the composition. Inconsideration of the effect of the content ratio of Si on the connectedform of an oxide cluster, In/Ga is preferably controlled to be, forexample, not less than 0.8 and not more than 2.0. In this case, theaverage coordination number of Ga in InGaSiO is 4.3 or more and theaverage coordination number of In is not less than 5.1 and not more than5.6 or less.

FIG. 8A to FIG. 8C and FIG. 9A and FIG. 9B are graphs showing simulationresults for the local structure of the oxide semiconductor according tothe first embodiment. These drawings illustrate the radial distributionfunction for InGaSiO having an amorphous structure. The horizontal axisrepresents an interatomic distance (unit: nm), and the vertical axisrepresents an RDF (Radial Distribution Function). The RDF is anabundance ratio normalized by the number of atoms. FIG. 8A shows adistance between an In atom and an O atom. FIG. 8B shows a distancebetween a Ga atom and an O atom. FIG. 8C shows a distance between an Siatom and an O atom.

As found from FIG. 8A to FIG. 8C, a bond distance of Si—O is theshortest in all models L, R, and U. The variance of interatomic distancebetween an Si atom and an O atom is extremely narrow as compared withthat between an In atom and an O atom and between a Ga atom and an Oatom. Such a radial distribution is an appropriate result reflecting theproperty of Si having a strong bonding strength to oxygen, andcontributes to improvement of heat resistance of the oxidesemiconductor. In the model R, a bond distance (peak value) between eachof an In atom, a Ga atom, and an Si atom and an O atom becomes thelongest. However, on the other hand, it was found that the variance ofinteratomic distance from a nearest neighbor O atom becomes the smallestin the model R.

FIG. 9A shows a distance between an In atom and an In atom. FIG. 9Bshows a distance between a Ga atom and a Ga atom. As found from FIG. 9A,the variance of interatomic distance between an In atom and an In atombecomes the smallest in the model R, and becomes the largest in themodel U. As found from FIG. 9B, the variance of interatomic distancebetween a Ga atom and a Ga atom becomes the smallest in the model R, andbecomes the largest in the model U.

From the simulation results of the radial distribution functiondescribed above, it is found that in InGaSiO having an amorphousstructure, the local structure geometrically changes depending on thecomposition, and there exists a proper value in the content ratio of Si.That is, by optimizing the compositions of the three elements of In, Ga,and Si, the local structure of InGaSiO can be controlled. According tothe embodiment, in the case where the content ratio of Si is set toapproximately 20 atomic % in the three elements of In, Ga, and Si, thevariance of interatomic distance is made small, and a structure havingexcellent short-distance order is obtained. On the other hand, in thecase where the content ratio of Si is set to approximately 11 atomic %in the three elements of In, Ga, and Si, a structure having a shortinteratomic distance is obtained.

FIG. 10A and FIG. 10B are graphs illustrating simulation results of theoxide semiconductor according to the first embodiment.

FIG. 10A shows a distribution of an angle (angle OInO) formed by an Inatom and O atoms, a distribution of an angle (angle OGaO) formed by a Gaatom and O atoms, and a distribution of an angle (angle OSiO) formed byan Si atom and O atoms in the model R having an amorphous structure inwhich the content ratio of Si is set to 20 atomic %. Incidentally, anangle ABC refers to an angle between a segment connecting A to B and asegment connecting B to C. The vertical axis in FIG. 10A represents anabundance ratio normalized by the number of O atoms present within arange (within a nearest neighbor) with a radius of 0.26 nm from eachatom with respect to each of an In atom, a Ga atom, and an Si atom.

As found from FIG. 10A, a steep peak is observed at 110° in the angleOSiO. It was found that the angle OSiO coincides with a typical bondangle (stable angle) in a regular tetrahedral structure. This result isconsistent with the result of the coordination number analysis.

FIG. 10B shows a distribution of an angle InOSi (an angle formed by anIn atom, an O atom, and an Si atom), and a distribution of an angleGaOSi (an angle formed by a Ga atom, an O atom, and an Si atom) in themodel R having an amorphous structure in which the content ratio of Siis set to 20 atomic %. The vertical axis in FIG. 10B represents anabundance ratio normalized within a range with a radius of 0.26 nmcentering on the O atom.

The angle InOSi corresponds to a connection angle of an In—O cluster andan Si—O cluster. The angle GaOSi corresponds to a connection angle of aGa—O cluster and an Si—O cluster. In each of the distribution of theangle InOSi and the distribution of the angle GaOSi, a significant peakis present, and therefore, in amorphous InGaSiO, as shown in a schematicview of FIG. 11, a structural body in which an In—O cluster and an Si—Ocluster are connected by sharing an O atom, and a structural body inwhich a Ga—O cluster and an Si—O cluster are connected by sharing an Oatom are presumed to be present. Incidentally, M shown in FIG. 11 is anIn atom or a Ga atom. An angle θ is an angle MOSi. That is, the angle θis a connection angle of an In—O cluster and an Si—O cluster or aconnection angle of a Ga—O cluster and an Si—O cluster. It is consideredthat in InGaSiO having an amorphous structure, each of an In atom and aGa atom is bonded to an Si atom by sharing an O atom. This resultcoincides with the result of the infrared absorption spectrum analysisshown in FIG. 3.

FIG. 12A to FIG. 12F are graphs showing simulation results of anelectronic state of the oxide semiconductor according to the firstembodiment.

FIG. 12A to FIG. 12C show the density of states (partial density ofstates: P-DOS (1/eV)) of the 5s orbital of In in the vicinity of theconduction band of amorphous InGaSiO. FIG. 12A, FIG. 12B, and FIG. 12Cshow the result of the model L, the result of the model R, and theresult of the model U, respectively. FIG. 12D to FIG. 12F show thedensity of states (partial density of states: P-DOS (1/eV)) of the 4sorbital of Ga in the vicinity of the conduction band of amorphousInGaSiO. FIG. 12D, FIG. 12E, and FIG. 12F show the result of the modelL, the result of the model R, and the result of the model U,respectively.

The Fermi energy is assumed to be 0 for convenience sake, and theconduction band minimum (CBM) is shown in the drawings. Although notshown in the drawings, the band gap defined by an energy differencebetween the valence band top and the conduction band minimum of InGaSiOis 3 eV in the model L, 3.2 eV in the model R, and 15 eV in the model Uand has a tendency to become larger with an increase in the contentratio of Si.

The conduction band minimum of InGaSiO is occupied mainly by the 5sorbital of In in all models. Since the 4s orbital of Ga is distributedin the energy band higher than the 5s orbital of In, the contribution ofthe 5s orbital of In to the carrier (electron) conduction is supposed tobe larger than the contribution of the 4s orbital of Ga to the carrier(electron) conduction. In an oxide semiconductor, the s orbital of ametal atom with a large principal quantum number greatly contributes tothe carrier conduction, and therefore, in particular, the electronicstate of the 5s orbital of In becomes an index when the carrierconduction is discussed.

As a result of comparison of the density of states in the 3 types ofcalculation models, it was found that the density of states of the 5sorbital of In becomes the highest in the model R in which the contentratio of Si is 20 atomic %. Further, it was found that the profile ofthe density of states of the 5s orbital of In in the model R has atendency to be distributed on a side of the conduction band minimum ascompared with the 5s orbital of In in the model L in which the contentratio of Si is low. In addition, it was found that the profile of thedensity of states of the 4s orbital of Ga in the model R has a tendencyto be distributed on a side of the conduction band minimum as comparedwith the 4s orbital of Ga in the model L in which the content ratio ofSi is low.

The density of states of an atomic orbital in the conduction band isderived from an interaction between neighboring atoms and the profile ofthe density of states is associated with the coordination structure ofan oxide cluster. Therefore, it is considered that as the short-rangeorder is excellent and the geometric position of atoms is more similar,the density of states of the conduction band becomes higher. Further, itis considered that when clusters having a low coordination structureexist more, the profile of the density of states is distributed morewidely on a side of the conduction band minimum.

In the model R in which the content ratio of Si is set to atomic %, thevariance of interatomic distance is the smallest and the short-rangeorder is excellent. Further in the model R, many In—O clusters in5-coordination and many Ga—O clusters in 5-coordination exist. For thisreason, in the model R, it is presumed that the density of states of the5s orbital of In becomes high and the profile of the density of statesof the 5s orbital of In is distributed on a side of the conduction bandminimum.

On the other hand, although not shown in the drawings, in the model U inwhich the content ratio of Si is set to 29.4 atomic %, it was found thatthe gap state derived from the 2p orbital of O occurs in the vicinity ofthe valence band top in spite of a low density. When considering theanalysis results of the coordination number, bond angle, connectionangle, and the like of InGaSiO, it is considered that the geometricbalance of the coordination structure was disrupted because Si was addedexcessively and distortion occurred in the local structure.

FIG. 13A to FIG. 13D are graphs showing simulation results of the oxidesemiconductor according to the first embodiment and an oxide of areference example.

FIG. 13A and FIG. 13B show an electronic state in the vicinity of theconduction band minimum in InGaSiO according to the embodiment, and FIG.13C and FIG. 13D show an electronic state in the vicinity of theconduction band minimum in InGaZnO according to the reference example.The Fermi energy is assumed to be 0 for convenience sake, and theconduction band minimum (CBM) is shown in the drawings.

Specifically, FIG. 13A and FIG. 13B show the results of the model R ofInGaSiO having an amorphous structure, and FIG. 13A shows the density ofstates of the 5s orbital of In and FIG. 13B shows the density of statesof the 4s orbital of Ga. As described previously, in the model R, thenumber of In atoms is 14, the number of Ga atoms is 14, the number of Siatoms is 7, and the number of O (oxygen) atoms is 56. The content ratioof Si is 20 atomic % (Si/(In+Ga+Si)=0.2). Each of Si/In and Si/Ga is0.5. In/Ga is 1.

FIG. 13C and FIG. 13D show the results of InGaZnO having an amorphousstructure, and FIG. 13C shows the density of states of the 5s orbital ofIn and FIG. 13D shows the density of states of the 4s orbital of Ga.This InGaZnO is a model simulating an actual sample formed by a DCmagnetron sputtering method using an InGaZnO target having a compositionof In:Ga:Zn=1:1:1. The number of atoms was determined based on theresult of the composition analysis, and the number of In atoms is 15,the number of Ga atoms is 13, the number of Zn atoms is 11, and thenumber of O (oxygen) atoms is 53. The number of O atoms is set to avalue that satisfies charge neutralization conditions.

From FIG. 13A and FIG. 13C, it was found that there is a possibilitythat the density of states of the 5s orbital of In of InGaSiO may becomehigher than the density of states of the 5s orbital of In of InGaZnO.From FIG. 13B and FIG. 13D, it was found that there is a possibilitythat the density of states of the 4s orbital of Ga of InGaSiO may becomehigher than the density of states of the 4s orbital of Ga of InGaZnO.

Although not shown in the drawings, InGaZnO is a structural body inwhich an In—O cluster and a Ga/Zn—O cluster are overlapped with a givenregularity (an edge-sharing structure or a corner-sharing structure).The coordination structure of the oxide cluster is distributed widelybetween 4 coordination (tetrahedron) and 6 coordination (octahedron).

On the other hand, InGaSiO is a structural body in which an In—O clusterand a Ga—O cluster are connected with a given regularity. In InGaSiO,each of the In—O cluster and the Ga—O cluster shares part of oxygenatoms with an Si—O cluster. For example, in the model R in which thecontent ratio of Si is set to 20 atomic %, the variance of interatomicdistance is small and the short-range order is excellent. Further, inthe model R, a probability that a geometrically similar oxide clusterexists is high.

It is considered that the density of states of the 5s orbital of In andthe 4s orbital of Ga mainly forming the conduction band of the oxidesemiconductor has a strong correlation with the short-range order in anamorphous local structure. Due to this, it can be interpreted that adifference in the structure of both models is reflected in theelectronic state. Therefore, in InGaSiO, by setting the compositions ofthe three elements of In, Ga, and Si to appropriate values, a morefavorable electronic state than that of InGaZnO can be obtained.

In InGaSiO, there is a positive correlation between the content ratio ofSi and the resistivity. When the content ratio of Si is increased, theresistivity increases, and when the content ratio of Si is decreased,the resistivity decreases. In the case where the oxide semiconductoraccording to the embodiment is applied to a channel layer of a thin filmtransistor, the resistivity of InGaSiO is desirably set within a properrange, and the content ratio of Si is preferably set within a range from9 atomic % to 22 atomic %. The content ratio of Si is preferably 10atomic % or more. Incidentally, in the case where the content ratio ofSi is less than 9 atomic %, the resistivity of InGaSiO is decreased toless than 1×10⁻⁴ Ωcm, and therefore, such a case is not preferred.

According to the embodiment, in the oxide semiconductor (InGaSiO)including In, Ga, Si, and O, heat resistance can be improved. Bycontrolling the compositions of the three elements of In, Ga, and Si tobe appropriate values, an oxide semiconductor whose heat resistance andcarrier conductivity are both high can be realized. Further, it becomeseasy to control the compositions of the constituent elements or thechemical bonding state, and the stability of the properties can beimproved.

Second Embodiment

FIG. 14 is a schematic sectional view illustrating a semiconductordevice according to a second embodiment.

As shown in FIG. 14, a semiconductor device 100 according to theembodiment includes a first semiconductor layer 50 (an oxidesemiconductor layer), a first conductive portion 70, a second conductiveportion 80, and a third conductive portion 30. The semiconductor device100 may include a substrate 10, a foundation film 20, an insulating film40, and a protective film 60. The first semiconductor layer 50 includesthe oxide semiconductor 55 according to the first embodiment. That is,as a material of the first semiconductor layer 50, the oxidesemiconductor 55 is used.

In this example, the semiconductor device 100 is a bottom-gate thin filmtransistor. For example, the first conductive portion 70 is a sourceelectrode, the second conductive portion 80 is a drain electrode, andthe third conductive portion 30 is a gate electrode.

The foundation film 20 is provided on the substrate 10. A directiondirected from the substrate 10 to the foundation film 20 is defined as aZ-axis direction (stacking direction). The foundation film 20 includesat least one of silicon oxide (SiO_(x)) and silicon nitride (SiN_(x)). Athickness in the Z-axis direction of the foundation film 20 isapproximately 100 nm.

The third conductive portion 30 is provided on the foundation film 20.For example, the third conductive portion 30 includes at least one oftungsten (W), molybdenum (Mo), copper (Cu), tantalum (Ta), and aluminum(Al). The third conductive portion 30 may include at least one oftitanium nitride (TiN) and tantalum nitride (TaN). The third conductiveportion 30 may include an aluminum alloy. The aluminum alloy includesaluminum as a main component. For example, a hillock is suppressed.

A thickness W1 in the Z-axis direction of the third conductive portion30 is not less than 10 nm and not more than 200 nm. A side surface ofthe third conductive portion 30 may be inclined with respect to theZ-axis direction. That is, the side surface of the third conductiveportion 30 may have a tapered shape. By forming the side surface of thethird conductive portion 30 into a tapered shape, the coverage by theinsulating film 40 formed on the third conductive portion 30 isincreased. By increasing the coverage, a leakage current can besuppressed.

The insulating film 40 is a gate insulating film. The insulating film 40is provided between the third conductive portion 30 and the firstsemiconductor layer 50. The insulating film 40 includes, for example, atleast one of silicon oxide (SiO_(x)), aluminum oxide (Al_(x)O_(y)),silicon nitride (SiN_(x)), and silicon oxynitride (SiO_(x)N_(y)). Theinsulating film 40 may include a plurality of films stacked on eachother. The plurality of films includes at least one of silicon oxide,aluminum oxide, silicon nitride, and silicon oxynitride. A thickness W2in the Z-axis direction of the insulating film 40 is not less than 10 nmand not more than 100 nm.

As shown in FIG. 14, the first semiconductor layer 50 includes a firstregion R01 (source region), a second region R02 (drain region), and athird region R03 (channel region). The third region R03 is providedbetween the first region R01 and the second region R02. A thickness W3in the Z-axis direction of the first semiconductor layer 50 is not lessthan 10 nm and not more than 100 nm. The first semiconductor layer 50includes a first surface 50 a and a second surface 50 b. The firstsurface 50 a is a surface on a side of the substrate 10, and the secondsurface 50 b is a surface on an opposite side to the first surface 50 a.

A direction directed from the first region R01 to the second region R02is defined as an X-axis direction (first direction). The Z-axisdirection is a direction perpendicular to the X-axis direction. At thistime, the third conductive portion 30 is separated from the third regionR03 in a direction crossing the X-axis direction (for example, theZ-axis direction). A part of the insulating film 40 is located in thethird region R03 and in the third conductive portion 30.

The protective film 60 is provided on the first semiconductor layer 50.The protective film 60 is a film that protects the second surface 50 bof the first semiconductor layer 50. For example, the protective film 60includes at least one of silicon oxide, aluminum oxide, and siliconnitride. The protective film 60 may be a film fabricated using TEOS(Tetra Ethyl Ortho Silicate). The protective film 60 may include aplurality of films stacked on each other. The plurality of filmsincludes, for example, at least one of silicon oxide, aluminum oxide,and silicon nitride. A thickness W4 in the Z-axis direction of theprotective film 60 is not less than 10 nm and not more than 200 nm.

The first conductive portion 70 is electrically connected to the firstregion R01. In this example, the first conductive portion 70 is providedon the first semiconductor layer 50 and the protective film 60. In thefirst conductive portion 70, a metal film including, for example, atleast one of molybdenum, titanium, tantalum, tungsten, and aluminum isused. The first conductive portion 70 may include at least one ofmolybdenum nitride (MoN), titanium nitride, and tantalum nitride. Thefirst conductive portion 70 may include a plurality of films stacked oneach other. The plurality of films includes at least one of theabove-mentioned conductive materials. In the first conductive portion70, a conductive oxide semiconductor thin film including ITO (Indium TinOxide) may be used.

The second conductive portion 80 is electrically connected to the secondregion R02. In this example, the second conductive portion 80 isprovided on the first semiconductor layer 50 and the protective film 60.In the second conductive portion 80, the same material as the materialof the first conductive portion 70 can be used. On the protective film60, the first conductive portion 70, and the second conductive portion80, an overcoat film may be provided. The overcoat film is, for example,a protective film. For example, in the overcoat film, the same materialas the protective film 60 can be used.

As described above, in a semiconductor device such as a transistor, theoxide semiconductor 55 according to the embodiment can be used.According to this, the heat resistance and the stability of theproperties of the semiconductor device can be improved.

FIG. 15 is a schematic sectional view illustrating another semiconductordevice according to the second embodiment.

A semiconductor device 120 shown in FIG. 15 includes a firstsemiconductor layer 51 in place of the first semiconductor layer 50described with respect to FIG. 14. The same description as that for theabove-mentioned semiconductor device 100 can be applied to thesemiconductor device 120 other than this. The first semiconductor layer51 includes a plurality of oxide semiconductor layers. The plurality ofoxide semiconductor layers is stacked in the Z-axis direction (adirection directed from a lower surface 51 a to an upper surface 51 b ofthe first semiconductor layer 51).

FIG. 16 is a schematic sectional view illustrating the firstsemiconductor layer of the semiconductor device according to the secondembodiment.

For example, the first semiconductor layer 51 includes a first layer51W1 and a second layer 51W2. The second layer 51W2 is stacked with thefirst layer 51W1 in the Z-axis direction. In this example, between twofirst layers 51W1, one second layer 51W2 is provided.

In other words, as shown in FIG. 16, the first semiconductor layer 51includes a first layer L1 (the first layer 51W1), a second layer L2 (thesecond layer 51W2), and a third layer L3 (the first layer 51W1). Thefirst layer L1 is provided between the third conductive portion 30 andthe second layer L2. The first layer L1 is in contact with, for example,the insulating film 40 (a first insulating film). The second layer L2 isprovided between the first layer L1 and the third layer L3. The thirdlayer L3 is provided between the protective film 60 (a second insulatingfilm) and the second layer L2. The third layer L3 is in contact with,for example, the protective film 60.

A thickness in the Z-axis direction of the first layer 51W1 is, forexample, approximately 10 nm, and a thickness in the Z-axis direction ofthe second layer 51W2 is, for example, approximately 15 nm. For example,the thickness of the second layer 51W2 is thicker than the thickness ofthe first layer 51W1.

The first layer 51W1 includes an oxide semiconductor 55 a, and thesecond layer 51W2 includes an oxide semiconductor 55 b. To each of theoxide semiconductor 55 a and the oxide semiconductor 55 b, the samedescription as that for the oxide semiconductor 55 according to thefirst embodiment can be applied. That is, each of the oxidesemiconductor 55 a and the oxide semiconductor 55 b is an oxideincluding In, Ga, and Si, and is, for example, a ternary oxide in anamorphous (non-crystalline) state. In each of the oxide semiconductor 55a and the oxide semiconductor 55 b, for example, 0.2<Si/In≦0.5,0.2<Si/Ga≦0.5, 0.09<Si/(In+Ga+Si)≦0.2, and 0.8≦In/Ga≦2.0.

For example, the content ratio of Si in the first layer 51W1 (oxidesemiconductor 55 a) is 20 atomic % (Si/(In+Ga+Si)=0.20), Si/In is about0.5, and Si/Ga is about 0.5. For example, the content ratio of Si in thesecond layer 51W2 (oxide semiconductor 55 b) is 11 atomic(Si/(In+Ga+Si)=0.11), Si/In is about 0.25, and Si/Ga is about 0.25.

In this manner, in the first semiconductor layer 51, a plurality ofoxide semiconductors in which the content ratio of Si (Si/(In+Ga+Si)) ismutually different is stacked. That is, the content ratio (a firstvalue) of Si in the first layer 51W1 (oxide semiconductor 55 a) isdifferent from the content ratio (a second value) of Si in the secondlayer 51W2 (oxide semiconductor 55 b). For example, the second value issmaller than the first value.

In the second layer 51W2, the content ratio of Si is low. Theresistivity in the second layer 51W2 is lower than the resistivity inthe first layer 51W1. Due to this, many of the carriers (electrons) inthe first semiconductor layer 51 are likely to flow in the second layer51W2. Therefore, an effect of an interface state (defect) present at aninterface between the insulating film 40 and the protective film 60 canbe relatively reduced. According to the embodiment, a variation in theelectrical properties of the semiconductor device 120 can be suppressed.

FIG. 17 is a schematic sectional view illustrating another firstsemiconductor layer of the semiconductor device according to the secondembodiment.

FIG. 17 shows another example of the first semiconductor layer 51described with respect to FIG. 15. The first semiconductor layer 51shown in FIG. 17 includes a first layer 51W3 and a second layer 51W4. Inthis example, four first layers 51W3 and three second layers 51W4 arealternately stacked in the Z-axis direction. A thickness along theZ-axis direction of each of the first layer 51W3 and the second layer51W4 is, for example, approximately 5 nm. Incidentally, the thickness ofthe plurality of layers included in the first semiconductor layer 51 maybe mutually different, and can be appropriately set as long as the totalthickness is, for example, 100 nm or less. The number of layers includedin the first semiconductor layer 51 is also arbitrary as long as thethickness of the first semiconductor layer 51 is 100 nm or less.

For example, the first layer 51W3 and the second layer 51W4 include theoxide semiconductor 55 a and the oxide semiconductor 55 b describedabove, respectively. That is, the content ratio of Si in the first layer51W3 is 20 atomic %, and the content ratio of Si in the second layer51W4 is 11 atomic %.

In the first layer 51W3 and the second layer 51W4, the content ratio ofSi is different. Therefore, in the first layer 51W3 and the second layer51W4, the structure of the oxide cluster or the band gap is different.In the case where the first layer 51W3 and the second layer 51W4 areperiodically stacked in the Z-axis direction, an interaction of eachoxide semiconductor layer becomes strong. Therefore, also in the casewhere the first semiconductor layer 51 shown in FIG. 17 is used, theheat resistance and the stability of the properties of the semiconductordevice can be improved. For example, the heat resistance, carrierconductivity, and resistivity (carrier concentration) can besimultaneously controlled, and a semiconductor device having morestabilized properties and high reliability is provided.

Third Embodiment

FIG. 18 is a schematic sectional view illustrating a solid-state imagingdevice according to a third embodiment.

As shown in FIG. 18, in a solid-state imaging device 150 according tothe embodiment, a light receiving portion 90 and an interconnect portion91 are provided. The solid-state imaging device 150 is, for example, aback-illuminated CMOS (Complementary Metal-Oxide Semiconductor) imagesensor. In the back-illuminated CMOS image sensor, light is incidentfrom an opposite side of a surface on which the interconnect portion 91is provided. On the light receiving portion 90, a color filter or alight gathering element such as a microlens can be provided.

The light receiving portion 90 is, for example, an epitaxial layerformed on a semiconductor substrate such as a silicon substrate. Thelight receiving portion 90 includes an n-type diffusion layer 90 n and ap-type region 90 p, and is provided with a photodiode PD. Theinterconnect portion 91 includes a multi-layer interconnect 92 and aninterlayer insulating layer 93. The multi-layer interconnect 92 isformed in the interlayer insulating layer 93.

In the photodiode PD, photoelectric conversion is performed. That is,light irradiated on the light receiving portion 90 is converted intocharges and stored. The n-type diffusion layer 90 n stores signalelectrons generated by photoelectric conversion. A transfer transistor94 is provided in the vicinity of an interface between the lightreceiving portion 90 and the interconnect portion 91, and signalelectrons stored in the n-type diffusion layer 90 n are moved to afloating diffusion layer FD.

A transistor group 95 is formed in the interconnect portion 91. Thetransistor group 95 includes a plurality of semiconductor devices(transistors). The transistor group 95 includes, for example, a resettransistor, an amplifier transistor, a selection transistor, etc., andamplifies the signal electrons and outputs them to the multi-layerinterconnect 92. As at least one of the plurality of semiconductordevices included in the transistor group 95, the semiconductor device100 or 120 described with respect to the second embodiment can be used.According to this, for example, high integration, high performance, andmultifunctionality can be achieved. Also in the solid-state imagingdevice 150, heat resistance and stability can be improved.

Fourth Embodiment

FIG. 19 is a schematic sectional view illustrating a semiconductormemory device according to a fourth embodiment.

FIG. 19 shows a portion of a semiconductor memory device 301(non-volatile memory) according to the embodiment.

The semiconductor memory device 301 includes a stacked body 320. Thestacked body 320 includes a plurality of conductive films 314 and aplurality of insulating films 315. The conductive films 314 and theinsulating films 315 are stacked along the Z-axis direction. By oneconductive film 314 and one insulating film 315, a unit structural bodyis formed. The conductive film 314 is formed of, for example, aconductive material such as polysilicon, and the insulating film 315 isformed of, for example, an insulating material such as silicon oxide.Each conductive film 314 is divided into a plurality of word lines 314 aextending in the X-axis direction.

In a portion 320 a of the stacked body 320, a silicon pillar 316extending in the Z-axis direction is provided, and the silicon pillar316 pierces the stacked body 320. Around the silicon pillar 316, amemory portion 317 (memory film) is provided. Therefore, a part of thememory portion 317 is disposed between the silicon pillar 316 and theword line 314 a.

The memory film 317 is a film capable of storing charges. For example,in the memory film 317, a tunneling insulating film, a charge storagefilm, and a block insulating film are stacked in this order from a sideof the silicon pillar 316. On a portion 320 a of the stacked body 320, abit line 318 extending in the Y-axis direction is provided. An upper endof the silicon pillar 316 is connected to the bit line 318 through aplug 319. A lower end of the silicon pillar 316 is connected to asubstrate (not shown).

A shape of an end portion 320 b of the stacked body 320 is a steppedshape in which a terrace 321 is formed for each unit structural bodycomposed of one conductive film 314 and one insulating film 315.

Incidentally, the terrace 321 is a part of an end portion in the X-axisdirection of the unit structural body. The terrace 321 includes a sidesurface 321 s of the unit structural body covered with an insulatinglayer 330 and a part of an upper surface 321 u of the unit structuralbody covered with the insulating layer 330. Incidentally, the sidesurface is a surface crossing the X-axis direction, and the uppersurface is a surface crossing the Z-axis direction. One terrace 321includes the side surface 321 s and the upper surface 321 u continuouswith the side surface 321 s. Then, a plurality of terraces 321 isarranged along the Z-axis direction. That is, the side surface 321 s andthe upper surface 321 u are alternately arranged along the Z-axisdirection.

The semiconductor memory device 301 includes a semiconductor device 101(transistor) provided on the end portion 320 b (terrace 321). Thesemiconductor device 101 includes a first semiconductor layer 50, afirst conductive portion 70, a second conductive portion 80, a thirdconductive portion 30, and an insulating film 40. The firstsemiconductor layer 50 is the same as the first semiconductor layer 50described with respect to FIG. 14. In the semiconductor device 101, theabove-mentioned first semiconductor layer 51 may be used in place of thefirst semiconductor layer 50.

The first semiconductor layer 50 of the semiconductor device 100 isseparated from the terrace 321 in the Z-axis direction. The insulatinglayer 330 is provided between the first semiconductor layer 51 and theterrace 321. A contact 327 extending in the Z-axis direction iselectrically connected to one conductive film 314 (word line 314 a). Thecontact 327 is electrically connected to the second conductive portion80 of the semiconductor device 101. The first semiconductor layer 50 iselectrically connected to an interconnect 326 through the firstconductive portion 70. The interconnect 326 is connected to a peripheralcircuit.

In this manner, also in the semiconductor memory device 301, thesemiconductor device including the oxide semiconductor according to theembodiment can be used. According to this, for example, high integrationcan be achieved, and the size of a chip can be reduced. Also in thesemiconductor memory device 301, heat resistance and stability can beimproved.

In the description of this application, the phrase “provided on” notonly includes a case of being provided in direct contact with, but alsoincludes a case of being provided by inserting another layer or filmtherebetween. In the description of this application, the phrase“electrically connected” not only includes a case of being connected indirect contact with, but also includes a case of being connected throughanother conductive member or the like.

Incidentally, in the description of this application, the term“perpendicular” not only includes strictly perpendicular, but alsoincludes a variation or the like in, for example, a manufacturingprocess, and may be substantially perpendicular and substantiallyparallel.

Hereinabove, embodiments of the invention have been described withreference to specific examples. However, embodiments of the inventionare not limited to these specific examples. For example, specificconfigurations of the respective components such as the firstsemiconductor layer, and the first to third conductive portions areincluded in the scope of the invention as long as the invention can becarried out in the same manner by appropriate selection from the rangeknown by those skilled in the art and the same effect can be obtained.

Further, a combination of two or more components of each of the specificexamples in the technically possible range is also included in the scopeof the invention as long as it includes the spirit of the invention.

In addition, all oxide semiconductors, semiconductor devices,semiconductor memory devices, and solid-state imaging devices that canbe carried out by appropriately modifying the design by those skilled inthe art based on the oxide semiconductors, semiconductor devices,semiconductor memory devices, and solid-state imaging devices describedabove as the embodiments of the invention also belong to the scope ofthe invention as long as they include the spirit of the invention.

In addition, it is understood that those skilled in the art can achievevarious variations and modifications in the range of the idea of theinvention and that these variations and modifications also belong to thescope of the invention.

While several embodiments of the invention have been described, theseembodiments are presented only as an example and are not intended tolimit the scope of the invention. The novel embodiments can be embodiedin various other forms, and various omissions, substitutions, andchanges can be made without departing from the spirit of the invention.The embodiments and modifications thereof are included in the scope andspirit of the invention and also included in the inventions described inthe claims and in the scope of their equivalents.

What is claimed is:
 1. An oxide semiconductor comprising: indium (In),gallium (Ga), and silicon (Si), a composition ratio of Si to In (Si/In)in the oxide semiconductor being larger than 0.2, and a compositionratio of Si to Ga (Si/Ga) in the oxide semiconductor being larger than0.2.
 2. The semiconductor according to claim 1, wherein a compositionratio of the Si to the In (Si/In) is 0.5 or less, and a compositionratio of the Si to the Ga (Si/Ga) is 0.5 or less.
 3. The semiconductoraccording to claim 1, wherein a composition ratio of the In to the Ga(In/Ga) is not less than 0.8 and not more than 2.0.
 4. The semiconductoraccording to claim 1, wherein a content ratio of the Si to a sum of acomposition of the In, a composition of the Ga, and a composition of theSi (Si/(In+Ga+Si)) is larger than 9 atomic % and not more than 20 atomic%.
 5. The semiconductor according to claim 1, wherein an averagecoordination number in a first coordination of the Ga is 4.3 or more,and an average coordination number in a first coordination of the In isnot less than 5.1 and not more than 5.6.
 6. The semiconductor accordingto claim 1, wherein the semiconductor includes at least one of anIn—O—Si bond or a Ga—O—Si bond.
 7. The semiconductor according to claim1, wherein the oxide semiconductor is amorphous.
 8. A semiconductordevice, comprising: a first semiconductor layer including the oxidesemiconductor according to claim 1, the first semiconductor layerincluding a first region a second region, and a third region providedbetween the first region and the second region; a first conductiveportion electrically connected to the first region; a second conductiveportion electrically connected to the second region; and a thirdconductive portion separated from the third region in a directioncrossing a first direction directed from the first region to the secondregion.
 9. The device according to claim 8, wherein the firstsemiconductor layer includes a first layer, and a second layer stackedwith the first layer in the crossing direction, a content ratio of Si inthe first layer to a sum of a composition of In in the first layer, acomposition of Ga in the first layer, and a composition of Si in thefirst layer (Si/(In+Ga+Si)) is a first value, a content ratio of Si inthe second layer to a sum of a composition of In in the second layer, acomposition of Ga in the second layer, and a composition of Si in thesecond layer (Si/(In+Ga+Si)) is a second value, and the first value isdifferent from the second value.
 10. The device according to claim 8,wherein a composition ratio of the Si to the In (Si/In) is 0.5 or less,and a composition ratio of the Si to the Ga (Si/Ga) is 0.5 or less. 11.The device according to claim 8, wherein a composition ratio of the Into the Ga (In/Ga) is not less than 0.8 and not more than 2.0.
 12. Thedevice according to claim 8, wherein a content ratio of the Si to a sumof a composition of the In, a composition of the Ga, and a compositionof the Si (Si/(In+Ga+Si)) is larger than 9 atomic % and not more than 20atomic %.
 13. The device according to claim 9, wherein the first layeris provided between the third conductive portion and the second layer,and the second value is smaller than the first value.
 14. The deviceaccording to claim 9, wherein the first layer is provided between thethird conductive portion and the second layer, and a resistivity of thesecond layer is lower than a resistivity of the first layer.
 15. Thedevice according to claim 9, wherein the first layer is provided betweenthe third conductive portion and the second layer, and a thickness ofthe second layer is thicker than a thickness of the first layer.
 16. Thedevice according to claim 13, further comprising: a first insulatingfilm provided between the first layer and the third conductive portion,the first layer being in contact with the first insulating film.
 17. Thedevice according to claim 9, wherein the first semiconductor layerfurther includes a third layer, the second layer is provided between thefirst layer and the third layer, and a content ratio of Si in the thirdlayer to a sum of a composition of In in the third layer, a compositionof Ga in the third layer, and a composition of Si in the third layer(Si/(In+Ga+Si)) is different from the second value.
 18. The deviceaccording to claim 17, further comprising: a second insulating film, thethird layer being located between the second insulating film and thesecond layer, and being in contact with the second insulating film. 19.A semiconductor memory device, comprising: the semiconductor deviceaccording to claim 8; and a memory portion.
 20. A solid-state imagingdevice, comprising: the semiconductor device according to claim 8; and alight receiving portion.